how do I solve the equation y''=-2y-y, and form a curved graph using a 2D lookup table

Given : y''+2y+y'=0, y(0)=1, y'(0)=1;

The script should calculate in detail the following: 1. Open the Simulink System 2. Calculate the parameters of Lookup Table: - the grid for the y values - the grid for the y' values - the grid of the right hand side function in this grid 3. define the initial values if the equation 4. set the parameters of the Lookup Table in the Simulink system.

If anyone can help, please do. Desperate, asked 5 professor already and still no luck. Please and Tq :)